The term “printing member” as used in the present document means any member for directly or indirectly transferring information onto a miscellaneous support by flexographic, copper-plate or offset printing. Consequently, a printing member comprises any one of the following elements: a printing cylinder in general such as a steel cylinder, a steel cylinder with chromium plated surface, a steel cylinder with rubber cladding, an aluminum cylinder with anodized or non-anodized surface; a printing sleeve to be mounted, in known manner such as by deformation with compressed air or by other means, on a mandrel (possibly of radially deformable type) rotating about its longitudinal axis, said printing sleeve being of composite material such as glass fiber, aramid fiber, carbon fiber or combinations of these fibers, said sleeve of fiber or composite material being clad with a polyurethane or rubber layer or presenting a chromium plated covering surface, or being clad with polyester or epoxy resin; a nickel sleeve unclad, or clad with rubber or polyurethane. Said printing member can present print characters on its outer surface (characters which may be directly formed on it or provided on plates or blocks fixed to said surface in any known manner) to consequently enable direct printing of said characters on a suitable support in a flexographic or copper-plate printing machine; alternatively said printing member can be used as a roller in an intermediate roller group of a flexographic, rotogravure, combining, spreading or offset machine to transfer ink in known manner onto a cylinder provided with said print characters, said roller hence enabling said characters to be indirectly printed on a suitable support.
In printing it has always been a problem for the user to associate with each printing member, information aimed at defining the physical characteristics (for example type, dimensions, characteristics of its constituent material or materials or of those of each cladding layer presented) or related to a previous use and such, for example, as to enable definition of a probable life span or of the need to subject said printing member to a mechanical operation (for example grinding) which would prolong its useful life. In general, this information (particularly if related to the physical characteristics of the printing member) is provided on labels or punchings that are separated from said printing member immediately prior to its initial use or which become illegible after a few uses.
There is therefore a need to provide a printing member, of which the information or data relevant to its use are always accessible to the user even after innumerable uses.
As noted above, a printing sleeve is one form of printing member. Printing sleeves are commonly used in a variety of applications, including flexographic and gravure printing for example. In particular, a printing sleeve that is generally cylindrical in shape can be mounted onto a rotatable printing cylinder of a printing machine for printing images onto a substrate. Most commercial printing machines have numerous printing cylinders and thus require numerous printing sleeves.
A variety of mechanisms can be used to mount the printing sleeve onto the printing cylinder. For instance, “air-mounting” is one common way of mounting a printing sleeve. Air-mounting generally refers to the placement of a printing sleeve onto a printing cylinder by supplying pressurized air between the sleeve and the cylinder. Typically, the printing sleeve has an inner surface diameter that is slightly smaller than the outer surface diameter of the printing cylinder. The difference in these diameters is a dimension known as the “interference fit”. Thus, by applying pressurized air, the diameter of at least the inner surface of the printing sleeve can be slightly expanded so that the sleeve can be mounted onto and/or removed from a printing cylinder. Maintaining the integrity of the interference fit is crucial to avoid slippage of the sleeve and resulting smearing or other unacceptable degradation of the image that is printed by the sleeve.
In some instances, an air-mountable printing sleeve can be formed from multiple concentric layers. In particular, most printing jobs involve an “image repeat”, which is the circumferential length of the image that is to be printed one or more times on a substrate. The circumference of a printing sleeve must be large enough to contain one or more image repeats. Moreover, different printing jobs may involve image repeats that differ in size, and consequently, different printing jobs may require printing sleeve repeats that also differ in size. For instance, a larger sleeve repeat size requires a printing sleeve with a larger circumferences or outer diameter for the same printing cylinder diameter.
To perform a job that requires a larger sleeve repeat size, the outer surface diameter of the printing sleeve must be large enough to yield the larger sleeve repeat size. Thus, printing sleeves resulting from multiple layers that increase the radial thickness of the sleeve are generally used to provide the necessary radial thickness. Specifically, the multi-layer printing sleeve has the effect of increasing the outer diameter of the sleeve to provide a larger repeat size so that the sleeve can be mounted on a smaller diameter printing cylinder that is already available in inventory. The thicker the sleeves then the greater the inertial mass of the rotating sleeve and the greater the danger of slippage if the interference fit should become compromised during the life of the sleeve.
For example, one type of multi-layered sleeve that is currently used in the art includes an innermost core layer that is formed from wound fiberglass coated with epoxy resin. After a first run of fiberglass tape coated with epoxy resin has been wound around a cylindrically shaped forming mandrel, a paper label having a thickness that is both uniform throughout the label and less than one millimeter is laid on this first run and covered with a second run of fiberglass tape coated with epoxy resin. Such label is provided with information concerning the ultimate sleeve that is to be formed. So typically, the innermost core layer would not be formed until it was known what type of sleeve was going to be built, so that the label could be created with the proper information and then embedded into the sleeve.
Subsequent runs of fiberglass tape coated with epoxy resin are successively wound around the length of the innermost core layer until the desired radial thickness of the innermost core layer has been attained for further processing. This desired radial thickness of this precursor stage of the innermost core layer will be larger than the ultimate desired radial thickness of the innermost core layer. In the further process of forming this innermost core, heat treatments that subject the innermost core layer to temperatures of about 90° C. for about two hours are required. Thereafter, the innermost core layer of this multi-layered sleeve must undergo mechanical grinding and polishing to prepare it for the application of one of the subsequent additional layers that will compose the final multi-layered sleeve. The addition of these subsequent layers typically will also involve heat treatments and mechanical operations of grinding and polishing. Such treatments and operations can subject the sleeve to various expansions, compressions and twisting contortions.
In addition to the innermost core layer, the prior art multi-layered sleeve also can contain one or more layers that add thickness to the sleeve. To form these additional layers, materials such as rigid polyurethane foam or other forms of polyurethane (e.g., ISA-PUR 2330 and ISA-PUR 2340 which are sold by H. B. Fuller Austria, NOMEX® which is sold by DUPONT, and honeycomb structures) are utilized by the prior art sleeve. The thickness of such additional layers can vary depending on the particular image repeat utilized. In addition, other outer layers are also sometimes disposed on the outer surface of these layers, thereby further increasing the inertial mass of the sleeve and placing more importance on maintaining the interference fit of the sleeve.
Gravure and flexographic printing machines can produce images that have multiple different colors. In mounting each printing sleeve on its mandrel of the printing machine for such multi-color printing jobs, it is important that each printing sleeve be mounted in registry with each other printing sleeve so that the final printed image with all of the colors does not have one colored portion of the image bleeding into another colored portion of the image. Registration of each printing sleeve must be achieved not only circumferentially but also axially (side-to-side on the mandrel). In a conventional printing sleeve that carries a printing plate for use in creating an image on a conventional flexographic printing machine or in a conventional printing sleeve that is etched with an image for use in a gravure printing machine, the printing sleeve has a notch in the sleeve. The mandrel has a pin, and the printing sleeve is mounted on the mandrel with the pin surrounded by the notch in the printing sleeve. Registration of each printing sleeve is thus achieved by locating the sleeve's notch relative to the mandrel's pin. The printing machine has an encoder on the servo-drive that indexes each mandrel so that the pin on mandrel points straight up at the 12 o'clock position at the beginning of each printing run of the machine. This is how the registration of the multi-color images is effected with conventional printing sleeves and printing machines.
However, as the sleeve is reused, the notch becomes wallowed out and cannot be reliably located relative to the pin on the mandrel. Indeed, the pin of mandrel can be broken off with careless handling of the sleeves. Each of these conditions of sleeve wear and pin damage renders the conventional manner of registration of the printing sleeve unacceptably inaccurate. Users of the printing sleeve must rely on less efficient methods for achieving the same registration of the sleeve on the mandrel of the printing machine. These less efficient methods can involve wastage of the underlying printing substrate during manual efforts to achieve the desired registration of the multiple color job on the substrate.